The chain-growth polymerization of a 1,1-diphenylethylene (DPE) derivative was achieved by employing addition–isomerization anionic polymerization. A homopolymer was obtained from the DPE monomer having a methyl group and a methoxy group on different phenyl groups, after the addition of s-butyllithium in the presence of tetramethylethylenediamine at 100 °C in a nonpolar solvent for 3 days. 1H and 13C NMR analyses of the obtained polymer indicated that the addition of a carbanion to the monomer resulted in the generation of a sterically hindered DPE anion. Subsequent isomerization by abstraction of the methyl proton on a phenyl group by the DPE anion formed a less hindered benzyl anion. In contrast, other DPE derivatives including those that had only a methyl group, only a methoxy group, or that had p-methyl and o-methoxy groups were unable to polymerize. These results indicate that both the o-methyl and o-methoxy groups were required to achieve this addition–isomerization polymerization.